What level does Venusaur learn frenzy plant?

OK

To teach venusaur/maganium/torterra frenzy plant, you need to beat the elite four, the weakest trainers in the world. Next you need to go to route 228 (check the map!) go straight ahead, don't cycle up any slopes, you will find a house, go inside it and talk to the old guy, he will tell you what to do.